Isolation of polysaccharide producers and heavy metal-tolerant local rhizobial isolates
Abstract
Background: Rhizobia are important soil bacteria that enter into a relationship with leguminous plants and fix nitrogen symbiotically. The importance of this relation is not only for soil as a soil fertilizer but also to keep our environment without pollution.
Methods: A Survey was conducted to collect different strains of rhizobial from different areas in Nineveh Governorate in Iraq. Isolation and biochemical tests were done under laboratory conditions. Determination of exopolysaccharide and tolerance to heavy metals was also conducted. Data obtained was recorded after cultivation and incubation of rhizobial strains.
Results: The rhizobial bacteria were isolated from the following leguminous plants: Vigna unguiculata L., Trifolium alexandrinum, Trigonella foenum-graecum L., Leucaena leucocephala L., Medicago sativa L., Phaseolus vulgaris L., Tribulus terrestris L., and Vicia faba L. Maximum exopolysaccharide production was reached at 3.76 gm/L by the isolate R. leguminosarum bv. Viciae RM25, after two days of incubation. The maximum cell dry weight was 3.50 gm/L. by the isolate E. meliloti RM5, after two days of incubation. The maximum reduction in pH was 4.80 by strain E. meliloti RM14, after two days of incubation. All the local isolated rhizobia were tolerant of nickel chloride for the studied concentrations: 100, 500, 1000, and 5000 µg/ ml. Also, we were tolerant to 100 and 500 µg/ ml of zinc sulfate and copper sulfate. All rhizobial isolates also tolerated a 1000 µg/ ml concentration of zinc sulfate.
Conclusion: Rhizobium bacteria possess several mechanisms that allow them to tolerate heavy metal exposure. These mechanisms include the expression of efflux pumps, the presence of metal-resistance plasmids, the production of EPS, and the ability to adapt to environmental factors. Further research is needed to fully understand the mechanisms behind the heavy metal tolerance in Rhizobium and to explore the potential applications of these bacteria in the bioremediation of heavy metal-polluted soils.
Keywords: Rhizobium; Isolation; Exopolysaccharide production; Heavy metal tolerance
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DOI: http://dx.doi.org/10.62940/als.v10i4.2314
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